Diffraction is a fundamental phenomenon of the propagation of wave energy fields such as, for example, electromagnetic or ultrasonic waves. Conventional methods of propagating energy waves are based on a simple solution to Maxwell's equation and the wave equation. Spherical or planar waveforms are utilized. Beams of energy will spread or diffuse as they propagate as a result of diffraction effects.
Present arrays are based on phasing a plurality of elements, all at the same frequency, to tailor the beam using interference effects. In a conventional antenna system, such as a phased antenna array driven with a monochromatic signal, only special phasing is possible. Resulting diffraction limited signal pulse beams begin to spread and decay when reaching a given length.
In many applications, it would be highly desirable to propagate a beam of wave energy over a long distance without an appreciable drop in the intensity of the beam. Such applications include, for example, radio microwave communication in which a non-divergent microwave beam would enable use of a smaller antennae, a decrease in the power of transmission, magnification of the mid-range of transmission, a decrease in the level of noise associated with transmission, and an increase in the confidentiality of the transmission. Further examples include use in radar, which would result in an increase in the range of the radar, a decrease in the required size of the radar, and a decrease in the power consumption of the radar. Still further examples include use in extremely long-range transmissions such as, for example, transmission between earth and satellites.
The traditional method of increasing the range of wave transmissions is to increase the size and power of the transmission into a wider beam or to utilize shorter wavelength transmissions. Increasing the width of the beam increases significantly the cost and power consumption required to transmit the beam while the use of shorter wavelengths such as x-rays is not practicable. Thus, over the past several years there has been significant efforts to increase the propagation and decrease the diffraction properties of wave beams.
One such attempt to reduce the diffraction of wave beams is to attempt to generate a wave packet with a broad frequency spectrum, referred to as an "electromagnetic missile." Electromagnetic missiles attempt to utilize a suitably tailored pulse shape which has an energy decay rate essentially limited by the highest frequencies present in the pulse generator. The high-frequency end of the pulse determines the furthest distance the missile can propagate. The generation and transmission of energy by electromagnetic missiles, however, has been severely limited in practice by the practical means of launching wave packets with extremely short rise times and pulse widths.
Another attempt to reduce diffraction of wave beams has been the use of a particular, monochromatic solution to the wave equation in a so-called "Bessel" beam. In this theoretical approach, the particular solution of the wave equation is diffractionless. The theoretical Bessel beam has an infinite number of lobes and therefore has infinite energy. Under the theoretical Bessel calculations, the energy content integrated over any lobe is approximately the same as the energy content in the central lobe. In practice, the lobes of the Bessel beam diffract away sequentially starting with the outer-most lobe. The central lobe persists as long as there are off-axis lobes compensating for the energy loss of the central lobe. However, the Bessel beam is not resistant to the diffractive spreading commonly associated with wave propagation. In fact, in practice a traditional Gaussian beam profile has been shown to be equally efficient to the Bessel beam profile.
Yet another attempt to reduce diffraction has been to use a particular parabolic approximation solution to the wave equation, known as an "electromagnetic directed energy pulse train." The pulses are produced by driving each element of an array of radiating sources with a particular drive function so that the results and localized packet of energy closely approximates this solution of the wave equation. However, further examination of this solution of the wave equation has demonstrated that the theoretical calculation of an improved Raleigh range was in error. The Raleigh range calculation was valid only at the pulse center and not across the width of the waist of the pulse. Appropriate calculation demonstrates that electromagnetic directed energy pulse trains do not defeat wave diffraction.
Yet another attempt to reduce diffraction has been to use a solution to the wave equation that is confined to a finite region of space in the wave zone, termed "electromagnetic bullets." This approach defines a radiation wave packet in the wave zone that is conformed to a suitable solid angle and extends over a finite radial extent to determine the sources required to generate the wave packet. However, this approach has not resulted in a computation that can solve the problem in a practical application.
What would thus be of great benefit would be a practical way to decrease divergence of propagated waves. To be practically applicable, such solution should apply new physical principals of compensation for the diffraction characteristics of wave propagation. The present invention achieves these objectives.